Method for Transmission/Reception of Contents Usage Right Information in Encrypted Form, and Device Thereof

1. A content usage right information providing device for providing content usage right information containing a content key for decrypting encrypted content data to a content usage right information receiving device, said content usage right information providing device comprising: an interface for controlling transmission/reception of data to/from said content usage right information receiving device; a cipher engine connected to the interface, comprising: a symmetric key creating unit for creating a first symmetric key, a second symmetric key and random number, each of which is a temporary key, for transmitting said content usage right information; a first encryption unit for encrypting data using a first public key set for said content usage right information receiving device; a second encryption unit for encrypting data using a second public key set for said content usage right information receiving device and a third public key created by said content usage right information receiving device; wherein the encryption is done with the second public key in which the random number created by the symmetric key creating unit is used and a fifth symmetric key is calculated in the encryption; a third encryption unit for encrypting data using said fourth symmetric key and a fifth symmetric key created by said content usage right information receiving device, and a decryption unit for decrypting encrypted data using said first symmetric key or said second symmetric key; and a controller connected to said cipher engine and said interface executing instructions for providing content usage right information, execution of the instructions causing the content usage right information providing device to perform operations comprising: receiving said first public key through said interface, and transmitting said first public key thus received, to said first encryption unit, creating said first symmetric key, and transmitting said first symmetric key thus created, to said first encryption unit, receiving said first symmetric key which has been encrypted using said first public key from said first encryption unit, and outputting encrypted first symmetric key thus received through said interface receiving said third symmetric key and said second public key, both of which have been concatenated and encrypted using said first symmetric key from said second encryption unit, through said interface, and transmitting said third symmetric key and said second public key which have been concatenated and encrypted thus received, to said decryption unit, creating said second symmetric key and said random number, and transmitting said second symmetric key and said random number thus created, to said second encrypting unit, outputting said second symmetric key which has been encrypted using said third symmetric key and said second public key, through said interface, receiving said fifth symmetric key, which has been encrypted using said first symmetric key or said second symmetric key through said interface, and transmitting said encrypted fifth symmetric key thus received, to said decryption unit, and receiving said content usage right information, which has been encrypted using said fourth symmetric key and said fifth symmetric key from said third encryption unit, and outputting said encrypted content usage right information thus received through said interface.

2. The content usage right information providing device according to claim 1 , wherein when said controller provides consecutively said content usage right information to said same content usage right information receiving device, said controller receives a new fifth symmetric key, which has been encrypted using said first symmetric key or said second symmetric key, and transmits said new encrypted fifth symmetric key to said second decryption unit and outputs encrypted content usage right information, which has been encrypted using said fourth symmetric key and said new fifth symmetric key, through said interface.

3. A content usage right information receiving device for receiving content usage right information containing a content key for decrypting and reproducing encrypted content data from a content usage right information providing device, said content usage right information receiving device comprising: an interface for controlling transmission/reception of data to/from said content usage right information receiving device; a cipher engine connected to said interface and the key holding units, comprising: a first public key holding unit for holding a first public key set for said content usage right information receiving device; a first private key holding unit for holding a first private key for decrypting encrypted data which has been encrypted using said first public key; a second public key holding unit for holding a second public key set for said content usage right information receiving device; a second private key holding unit for holding a second private key for decrypting encrypted data which has been encrypted using said second public key; a symmetric key creating unit for creating a first symmetric key and a second symmetric key, each of which is a temporary key, at the time of reception of content usage right information from said content usage right information providing device; an encryption unit for encrypting data using said third symmetric key or a fourth symmetric key, each of which have been created by said content usage right information providing device; a first decryption unit for decrypting encrypted data, which has been encrypted using a first public key, using said first private key; a second decryption unit for decrypting data, which has been encrypted using a second public key and said first symmetric key; wherein a fifth symmetric key is calculated with said second public key and an encrypted data, which has been encrypted using said second symmetric key; and a third decryption unit for decrypting encrypted data, which has been encrypted using said second symmetric key and said fifth symmetric key, using said second symmetric key and said fifth symmetric key; a controller connected to the cipher engine and said interface, executing instructions for receiving content usage information execution of the instructions causing the content usage right information receiving device to perform operations comprising: outputting said first public key through said interface, receiving said third symmetric key, which has been encrypted using said first public key, through said interface, and transmitting said encrypted third symmetric key thus received, to said first decryption unit, creating said first symmetric key, concatenating said created first symmetric key and said second public key, and transmitting said first symmetric key and said second public key, which have been concatenated, to said encryption unit, receiving said first symmetric key and said second public key, which have been encrypted using said third symmetric key, from said encryption unit, and outputting said first symmetric key and said second public key which have been encrypted, through said interface, receiving said fourth symmetric key, which has been encrypted using said first symmetric key and said second public key, through said interface, and transmitting said encrypted forth symmetric key thus received, to said second decryption unit, creating said second symmetric key, and transmitting said second symmetric key thus created, to said encryption unit, receiving said second symmetric key, which has been encrypted using said third symmetric key or said fourth symmetric key decrypted by said first decryption unit or said second decryption unit, from said encryption unit, and outputting encrypted second symmetric key thus received through said interface, and receiving encrypted content usage right information, which has been encrypted using said second symmetric key and said fifth symmetric key, through said interface, and transmitting said encrypted content usage right information to said third decryption unit, and receiving said content usage right information from said third decryption unit.

4. The content usage right information receiving device according to claim 3 , wherein when said controller receives consecutively said content usage right information from said same content usage right information providing device, said controller instructs said symmetric key creating unit to create a new second symmetric key; said controller outputs said new second symmetric key, which has been encrypted by said encryption unit using either said third symmetric key or said fourth symmetric key, through said interface; said controller receives encrypted content usage right information, which has been encrypted using said new second symmetric key and said fifth symmetric key, through said interface.